1. Field of the Invention
The present invention relates to an engine control method and device, and more particularly to an engine control method and device in a system having a first manifold pressure sensor and a second manifold pressure sensor serving as a backup for the first manifold pressure sensor, in which the operation of the system can be continued even when both of these two sensors have failed.
2. Description of Background Art
In a conventional engine control system, many sensors are used and a failure diagnosing system for diagnosing whether or not these sensors are normal is known. For example, Japanese Patent Laid-open No. 2003-307152 discloses a method including the steps of determining whether or not an output signal from a sensor for detecting a pressure in an intake manifold falls within a preset range, calculating a pressure in the intake manifold according to engine operating conditions, and determining whether or not the difference between the detected intake manifold pressure indicated by the output signal from the sensor and the calculated intake manifold pressure is less than a preset value in the case that the output signal from the sensor falls within the above preset range, wherein when the output signal from the sensor does not fall within the above preset range or when the above difference is not less than the above preset value, the calculated intake manifold pressure is set as an intake manifold pressure.
Further, Japanese Patent Laid-open No. Hei 10-176582 discloses an electronically controlled throttle device having two sensor systems each having an accelerator sensor, throttle sensor, etc. for the purposes of fail-safe sensing or the like, in which failure diagnosis is performed by comparing sensor outputs from these two sensor systems. For example, it is determined whether or not the throttle sensor is abnormal by comparing a deviation in sensor output between a main throttle sensor and a sub-throttle sensor with a threshold value.
As to a failure such as breaking of a wire and short circuit, of sensor system failures, the abnormality of any sensor can be determined when an output value from the sensor is greater than or less than a predetermined value or a predetermined range, and a predetermined operation against this abnormality can be performed. However, although the sensor output value falls within the predetermined range, there is a case that the abnormality due to a change or deterioration in output characteristics of the sensor cannot be determined. For example, in controlling an engine for an aircraft, a stricter standard for the accuracy of failure diagnosis is provided, so that there is a case that the conventional failure diagnosing method is insufficient.
In the failure diagnosing method described in Japanese Patent Laid-open No. Hei 10-176582, the failure of one of the two sensor systems can be detected. However, no measures against the failure of both of the two sensor systems are taken.